The nature of the oil and gas industry is such that a wide variety of materials, including solids, liquids, and gases need to be transported through different sorts of pipes under a wide variety of conditions. One feature that all these pipes share is that they must be made from materials that are impermeable and resistant to the substances being transported. Such substances can include not only hydrocarbons, but water and salt water.
For example, drilled oil wells are typically lined with steel casings. The steel is susceptible to erosion and corrosion, however, and, as a result, these pipes have been lined with plastic liners in both onshore and offshore pipelines. The casing liner must be capable of withstanding temperatures and pressures typically encountered in oil and gas wells, and must have compression and-memory properties that allow it to be downsized for insertion into the casing and subsequently permit it to expand to form a fluid tight seal against the casing. Polyethylene pipe is considered to be the preferred material for the fabrication of the casing. In addition to its good compression and memory properties, polyethylene pipe is resistant to abrasion, which enables it to withstand the passage of downhole tools, and resistant to salt water and some chemical corrosion. Furthermore, polyethylene pipe can be formed into a long, continuous tube containing no joint connections. This is important in that many casing leaks occur in or near the connection between one segment of casing and another. However, for high temperature and aggressive chemical environments, nylon 11 is often used. Performance is much improved, but the cost is such that nylon 11 is only considered for highly demanding applications.
A method for lining steel casings used in well-drilling operations, preferably with polyethylene, for purposes of corrosion protection has been disclosed in Vloedman, U.S. Pat. No. 5,454,419. A procedure is described for reducing a continuous string of polyethylene pipe in diameter and then running it into a casing-lined well bore in such a manner that the polyethylene pipe remains in a reduced state until the polyethylene pipe reaches a pre-selected depth. After the polyethylene pipe is run to the desired depth, the reduced pipe is allowed to rebound, thereby forming a fluid-tight seal with the casing and effectively sealing any breaches in the casing.
While the method disclosed in U.S. Pat. No. 5,454,419 patent has successfully met the need for repairing breaches in casings in an effective and time efficient manner, several inefficiencies have nevertheless been encountered, particularly in circumstances when only a selected segment of the casing is in need of repair. If only a relatively short section of approximately 100 to 2000 feet of casing is in need of repair and this section is located several thousand feet below the surface, for example, it is more cost effective if the casing does not have to be lined entirely from the surface to the pertinent section, and U.S. Pat. No. 6,283,211, also by Vloedman, discloses a method of repairing portions of a pipe.
In other known liner systems, the liner resides in close-tolerance with the host pipe along its length, forming a stable composite system. The installed liner may be either loose-fit or compressed-fit. In all but low pressure applications, the stresses induced by fluid pressure from within the liner are transmitted to the surrounding host tubular and the host tubular resists these transmitted stresses. As hydrocarbon fluids permeate through the liner, there is a resulting build up of pressure in the annulus (the space between the liner and the inside surface of the host pipe) which can directly result in corrosion, leakage and/or liner collapse if the pressure inside the pipe drops below that of the annulus. All are major deficiencies. Where the liner outer surface maintains a significant degree of contact with the inner host wall there is a significant degree of sealing. The annular cross sectional area is thus reduced to the extent that only an extremely tortuous path for the annular fluid's migration toward any venting mechanism along the system exists.
U.S. Pat. No. 6,220,079 (Taylor), addresses this problem by disclosing a method of decreasing the negative effects of pressure in the annulus by modification of the liner configuration from its usual uniform cylindrical shape to include the incorporation of multiple conduits between the liner and the host tubular. These conduits provide a relatively inexpensive means for venting the pressure, which can help prevent liner collapse, and also permit the introduction of instruments for making measurements.
Other contributors to the onset of liner collapse include the liner's mechanical properties, the nature of the fluid transported, pressure, temperature, and the effective rate of fluid permeation. The present invention discloses a method of addressing liner collapse by significantly decreasing the rate of fluid permeation through the liner.
U.S. Pat. No. 6,127,478 (Spohn) discloses a melt-mixed blend comprising a blend of polar-grafted fluoropolymer well-dispersed in an incompatible polyamide. This technology requires high shear and high mixing to obtain the well-dispersed blend.
It is an object of the present invention to provide pipes and liners with good permeation resistance to hydrocarbons. A feature of the present invention is to melt blend at least one polyamide and at least one grafted fluoropolymer having polar functionality in the process of forming the pipes and liners. It is an advantage of the present invention to provide pipes and liners comprising a polymeric material that has enhanced barrier properties relative to polyamides. A further advantage of the invention is to provide fuel lines with improved resistance to hydrocarbon permeability. These and other objects, features, and advantages will become better understood upon having reference to the detailed description herein.